Apparatus for copying an electrostatic charge pattern in intensified form

ABSTRACT

Apparatus for reproducing, on an electrically insulating film, an electrostatic charge pattern in an intensified form comprises two cylinders, disposed parallel to each other, and apparatus to reciprocate them in opposite directions of rotation with respect to each other. The image- bearing surface is on one cylinder; and the film, on which the charge pattern is to be reproduced, has opposite ends secured to the two cylinders, respectively. Grounded wetted sponges are disposed adjacent opposite surfaces of the film so as to first induce a monopolar charge pattern on the film, during one direction of rotation of the cylinders, and then to induce a bipolar pattern on the film, during an opposite direction of rotation of the cylinders.

United States Patent [191 Kiess [4 1 Sept. 16, 1975 [75] Inventor: Helmut Gustav Kiess, Zurich,

Switzerland [73] Assignee: RCA Corporation, New York, NY.

[22] Filed: Aug. 9, 1974 21 1 Appl. No.1 496,359

[56] References Cited UNITED STATES PATENTS 3,582,731 6/1971 Sato 317/262 A 3,776,634 12/1973 Williams. 355/133 3,838,918 10/1974 Fisher 355/3 R Primary Examiner-Bernard Konick Assistant Examiner.lay P, Lucas Attorney, Agent, or Firml-l. Christoffersen; R. P. Williams; A. l. Spechler 5 7] ABSTRACT Apparatus for reproducing, on an electrically insulating film, an electrostatic charge pattern in an intensified form comprises two cylinders, disposed parallel to each other, and apparatus to reciprocate them in opposite directions of rotation with respect to each other. The image bearing surface is on one cylinder; and the film, on which the charge pattern is to be reproduced, has opposite ends secured to the two cylinders, respectively. Grounded wetted sponges are disposed adjacent opposite surfaces of the film so as to first induce a monopolar charge pattern on the film, during one direction of rotation of the cylinders, and then to induce a bipolar pattern on the film, during an opposite direction of rotation of the cylinders.

6 Claims, 9 Drawing Figures FATENTEBSU re 5975 snwimz PATENTED SEP 1 6 I975 sum 2 0; 2

APPARATUS FOR COPYING AN ELECTROSTATIC CHARGE PATTERN IN INTENSIFIED FORM This invention relates to apparatus for reproducing, on an electrically insulating film, an electrostatic charge pattern in an intensified form conforming substantially in configuration to an original electrostatic charge pattern on an electrically insulating imagebearing surface. The novel apparatus is particularly useful in the electrostatic and the electrophotographic printing arts for increasing the intensity of latent electrostatic images prior to their detection and/or their development to render them visible.

The sensitivity of an electrophotographic or electrostatic printing process is limited by the charge density of electrostatic charge patterns (latent images) produced on an image-bearing surface of a recording element. The lower the charge density at which a photoconductor, for example, is operable, the lower is the number of photons needed to discharge the electrostatically charged photoconductor. A low charge density electrophotographie process is, therefore, synonomous with high sensitivity electrophotography. On the other hand, the detection and/or the development of low charge density electrostatic charge patterns with a high resolution present serious difficulties. It is highly desirable, therefore, to intensify the latent electrostatic charge patterns prior to their further processing.

It has been proposed, in US. Pat. No. 3,776,634 for Apparatus For And Method Of Reproducing An Elec trostatic Charge Pattern, to produce, on a collector plate, an intensified electrostatic charge pattern of an original electrostatic charge pattern on an imagebearing surface with the aid of a transfer sheet. In this prior-art method both the transfer sheet and the collector plate have a plurality of discrete areas of electrically conductive material thereon; and an intensified elec trostatic charge pattern is formed on the collector plate by periodically inducing charge patterns on the transfer sheet and transferring each of the induced charge patterns completely to the collector plate. While apparatus utilizing this prior-art method is useful for many application, it requires a transfer sheet and a collector plate of special construction.

The novel apparatus utilizes insulating films readily available on the commercial market, requiring no special structure.

Briefly, the novel apparatus comprises first and second rotary members having axes disposed substantially parallel to each other. Means are provided to reciprocate the direction of relative rotation of the rotary members. The direction of relative rotation of the first rotary member is simultaneously opposite to that of the second rotary member. The image-bearing surface is on at least a portion of the first rotary member; and the film is secured between the first and second rotary members. Thus, when relative rotary reciprocating motion is produced between the rotary members, the film is first disposed over the image-bearing surface, in one direction of reciprocation, and then separated from the image-bearing surface, in the other direction of reciprocation. One source of charge migration is disposed to contact one surface of the film so as to induce thereon a monopolar charge pattern, as the film moves into contact with the image-bearing surface. Another source of charge migration is disposedadjacent to an opposite surface of the film, to induce a bipolar charge pattern thereon when the film is being separated from the imagebearing surface. Thus, the intensity of the charge patterns on the film increases as the rotary members are reciprocated.

The novel apparatus of the present invention will be explained with the aid of the accompanying drawings in which:

FIG. 1 is a side elevation of a recording element, having an electrically insulating image-bearing surface,

and showing an original electrostatic charge pattern of negative polarity thereon;

FIGS. 2 and 4 are scehmatic drawings of an electrically insulating film, in side elevation in an area of influence of the original electrostatic charge pattern on the image-bearing surface shown in FIG. 1, and in the operation of inducing monopolar electrostatic charge patterns on the upper surface of the film;

FIGS. 3 and 5 are schematic drawings of the electrically insulating film, in side elevation, in the operation of converting monopolar charge patterns on the film to bipolar charge patterns;

FIG. 6 is a side elevational view of rotary members in one embodiment of the novel apparatus in the operation of bringing the film into contact with the imagebearing surface, during one direction of reciprocation of the rotary members;

FIG. 7 is a side elevational view of the rotary members shown in FIG. 6 in the process of separating the film from the image-bearing surface during an opposite direction of reciprocation of the rotary members;

FIG. 8 is a fragmentary perspective view of a portion of one of the rotary members, in another embodiment of the novel apparatus, showing sprocket means for keeping the film aligned on the rotary members; and

FIG. 9 is one embodiment of reciprocating means to be coupled to the rotary members for reciprocating them in accordance with the present invention.

The apparatuses in FIGS. 1-5 illustrate the method of reproducing, on an electrically insulating film, an electrostatic charge pattern in intensified form conforming substantially in configuration to an original electrostatic charge pattern on anelectrically insulating image-bearing surface. Referring particularly to FIG. 1 of the drawing, there is shown a recording element 10 having an image-bearing surface 11 on which there is an original electrostatic charge pattern of negative polarity. It is, however, within the contemplation of the present invention for the original charge pattern to be of either or both polarities. The original electrostatic charge pattern on the image-bearing surface 11 is a monopolar electrostatic charge pattern that can be produced thereon in many different ways. For example, the recording element 10 can be a sheet or film of electrically insulating plastic material, such as MYLAR (trademark for Dupont de Nemours), and the electrostatic charge pattern on the image-bearing surface 11 can be produced thereon by a method described in a copending patent application, Ser. No. 451,093 now US. Pat. No. 3,872,480, for A Method Of Electrostatic Recording On Electrically Insulating Film By Non-Wetting Electrically Conductive Liquids. The original charge pattern on the image-bearing surface 11 can also be applied to the recording element 10 in a method described for inducing a monopolar charge pattern on an insulating transfer sheet (film) in the aforementioned US. Pat. No. 3,776,634.

The electrostatic charge pattern on the imagebcaring surface 11 may be of such low intensity that it may be desirable to intensify a reproduction thereof so that it may be suitably detected and/or developed. The first step in the method also employed by the novel appara tus) is to place a film 12 (FIG. 2) of electrically insulating material in an area of influence of the original charge pattern on the image-bearing surface 1 1. Preferably, one (lower) surface 13 of the film 12 is placed in contact with the (upper) image-bearing surface 11 of the recording element 10. In FIG. 2, as in FIG. 4, the film 12 is shown spaced from the recording element 10 to show clearly the electrostatic charges on the adjacent surfaces of the recording element 10 and the film 12. In practice, however, it is preferable for the surface 13 of the film 12 to Contact the image-bearing surface 11 of the recording element 10.

Means are provided to produce a monopolar charge pattern on the upper surface 14 of the film 12, of opposite polarity to that of the original electrostatic charge pattern on the image-bearing surface 11. To this end, a source of charge migration, such as a sponge 15, wetted with a conductive fluid or liquid 16, is electrically connected to a common electrical connection, such as a bias of ground potential, as shown in FIG. 2. The conductive liquid 16, such as water, methanol, or ethanol, for example, is substantially non-wetting on the film 12. Thus, with the lower surface 13 of the film 12 in intimate Contact with the image-bearing surface 11 of the recording element 10, a monopolar (positive) electrostatic charge pattern is induced on the upper surface 14 of the film 12 by momentarily wiping all areas of the surfaces 14 with the grounded wetted sponge 15, as by moving the sponge 15 over all areas of the surface 14 in the direction of the arrow 17.

The electrically insulating film 12 is removed from the recording element 10; and the monopolar (positive) electrostatic charge pattern thereon is converted to a bipolar charge pattern, as shown in FIG. 3, by moving the grounded wetted sponge l momentarily over all areas of the lower surfaces 13 of the film 12 in the direction of the arrow 17. Thus, as shown in FIG. 3, the film 12 has a bipolar charge thereon and is, therefore, neutral to the outside world.

An additional monopolar (positive) electrostatic charge pattern is now superimposed over the bipolar charge pattern on the film 12, by the operation shown in FIG. 4. To this end, the lower surface 13 of the film 12 is placed onto intimate contact with the image bearing surface 11 of the recording element so that the electrostatic charge patterns of the same (negative) polarity are superimposed upon each other in register, and all areas of the upper surface 14 are wiped momentarily with the grounded wetted sponge 15 in the direction of the arrow 17. The film 12, shown in FIG. 4, now has an additional (positive) monopolar electrostatic charge pattern added to the bipolar charge pattern already on the film 12.

In the next operation, the newly added monopolar charge pattern on the film 12 is converted to a bipolar electrostatic charge pattern, as shown in FIG. 5. This is accomplished by separating the film 12 from the element 10 and moving the grounded wetted sponge 15 momentarily over all areas of the lower surfaces 13 of the film 12 in the direction of the arrow 17. It will now be observed looking at FIG. 5, that the upper and lower surfaces 14 and 13 of the film 12 are charged with elec- 4 trostatic charge patterns of opposite polarity, and that the intensity of each electrostatic charge pattern is greater than that of the original electrostatic charge pattern on the image-bearing surface 11 of the recording element 10 shown in FIG. 1.

If it is desired to intensify the electrostatic charge patterns on the surfaces 13 and 14 of the film 12 still further, the aforementioned steps of adding a monopolar electrostatic charge pattern to the bipolar charge pattern already on the film l2, and then converting the monopolar charge pattern to a bipolar charge pattern, again, can be repeated. The novel apparatus of the present invention performs the operations of the method described supra sequentially and automatically.

Referring now to FIG. 6, there is shown one embodiment of a novel apparatus 20 for reproducing an original electrostatic charge pattern in intensified form. The apparatus 20 comprises lower and upper rotary members 22 and 24, respectively, such as cylindrical rollers of electrically insulating material disposed substantially parallel to each other. The rotary members 22 and 24 may be made of insulating plastic material such as Ny- Ion or Teflon, for example, and are disposed for rotation on shafts 26 and 28, respectively. The axes of the shafts 26 and 28 are also parallel to each other, Means, to be described hereinafter, are coupled to the shafts 26 and 28 to reciprocate the rotary members 22 and 24 simultaneously in opposite directions of rotation. Thus, as shown in FIG. 6, when the rotary member 22 is rotated in the direction of the arrow 30, the rotary member 24 is rotated simultaneously in the direction of the arrow 32.

A recording element, such as the recording element 10 in FIG. I, is secured to the surface of the rotary member 22 by any suitable means, such as by screws 34 and 36. Thus, the image-bearing surface 11 of the re cording element 10 forms the outer surface of the rotary member 22. It is also within the contemplation of the present invention for the outer surface of the rotary member 22 to be any electrically insulating surface that is integral with the rotary member 22 and is capable of retaining an electrostatic monopolar charge pattern.

The electrically insulating film 12, shown in FIG. 3, is secured between the rotary members 24 and 22. Hence, one end 38 of the film 12 is secured to the rotary member 24 by any suitable means, as by screws 40; and an opposite end 42 of the film 12 is secured to the rotary member 22 adjacent an end of the recording element 10, by any suitable means, as by screws 44. The surface 14 of the film 12 is disposed against the surface of the rotary member 24, and the film 12 is secured to the rotary member 22 in a manner so that the surface 13 of the film 12 will be superimposed over the imagebearing surface 11 of the recording element 10 when the rotary members 22 and 24 are rotated simultaneously in the directions of the arrows 30 and 32, respectively. Hence, the rotary members 22 and 24 provide means for superimposing the film 12 on the imagebearing surface 11, in one direction of reciprocation of the rotary members 22 and 24.

means are provided to apply a source of charge migration to the surface 14 of the film 12 when the film 12 is moved into Contact with the image-bearing surfade 11, the latter having the original electrostatic charge pattern thereon. To this end, there is provided an elongated electrically conductive receptacle 64 having a wetted sponge a therein that is being urged against the surface 14 of the film12 by a spring 48. The receptacle 46 is-grounded. The wetted-and grounded sponge 15a functions as a source of charge migration in the same manner as described for the sponge 15 in FIG. 2.

Means are provided to convert the monopolar charge pattern induced on the film' 12 by the grounded and wetted sponge 15a to a bipolar charge pattern. To this end, a wetted sponge 15!), similar to the wetted sponge 15a, is disposed in an elongated receptacle 50 of electrically conductive material which is also grounded. The sponge 15b is urged against the surface 13 of the film 12 by a spring 52.

Referring now to FIG. 7, the rotary members 22 and 24 are shown in the operation of being rotated in the opposite direction of reciprocation to that shown in FIG. 6. Looking at FIG. 7, the rotary members 22 and 44 are shown in the operation of being rotated simultaneously in the directions 54 and 56, respectively. During this last operation, the film 12 is separated from the imagebearing surface 1 l of the recording element 10. During the separation of the film 12 from the recording element 10, the surface 13 of the film 12 is wiped momentarily with the grounded wetted sponge 15b, thereby converting the monopolar charge pattern previously applied to the surface 14 of the film 12 to a bipolar pattern, as shown, for example, in FIG. 3.

By repeatedly reciprocating the rotary members 22 and 24 first in the directions 30 and 32, as shown in FIG. 6, and then in the directions 54 and 56, as shown in FIG. 7, monopolar electrostatic charge patterns are applied to the surface 14 of the film 12 and then con verted to bipolar charge patterns by balancing the monopolar charge patterns with charge patterns of opposite polarity on the surface 13 of the film 12. Hence, by reciprocating the rotary motion of the rotary mem bers 22 and 24 a plurality of times, the intensity of the electrostatic charge patterns on the surfaces 13 and 14 of the film 12 is increased. The maximum charge den sity of the charge patterns is determined by the breakdown strength and the dielectric constant of the film 12.

Referring now to FIG. 8 of the drawing, there is shown another embodiment of the novel apparatus wherein a film 12a, substantially similar to the film 12 in FIGS. 6 and 7, is formed with a plurality of holes 60 adjacent opposite edges (only one edge shown in FIG.

8) to receive a plurality of sprockets 62 therein for aligning the film 12a on a rotary member 24a. The rotary member 24a is substantially similar to the rotary member 24, except for the attached sprockets, and the film 12a is adapted to engage a lower rotary member (not shown) similar to the rotary member 22 but also formed with sprockets to engage the holes 60. The recording element 10 may also be formed with holes along its edges to those illustrated in the film 12a, for good alignment on the rotary member and for engage ment in register periodically with the film 12a.

Means, shown in FIG. 9, are provided to reciprocate the rotary members 22 and 24 in opposite directions of the rotation with respect to each other. In one embodiment of the reciprocating means, a gear 64 is coupled to the shaft 26 of the rotary member 22, and a gear 66 is coupled to the shaft 28 of the rotary member 24. The gears 64 and 66 are engaged to reciprocate the gears 64 and 66 by motion imparted to it by a pinion shaft 70 fixed to a wheel 72. The rack 68 is integral with a slotted yoke 74;, and the pinion shaft is disposed within the slot 75 of the slotted yoke 74 so as to reciprocate the rack 68' in bearings 76 and 78 when the ,wheel 72 is rotated about its center, as by a motor 80 coupled to a shaft 82 fixed to the wheel 72. It is also within the contemplation'of the present invention. for the rotary members:22 and 24 tobe reciprocated by any other suitable means known in the art. The rotary members 22 and'24 are never rotated more than one revolution in any direction of reciprocation. I

What is claimed is: t Y 1. Apparatus for reproducing, on an-electrically insulating film, an electrostatic charge pattern in an intensified form conforming substantially in configuration to an original electrostatic charge pattern on an electrically insulating image-bearing surface, said apparatus comprising:

first and second rotary members having axes disposed substantially parallel to each other, means to dispose said image-bearing surface on at least a portion of said first rotary member, means coupled to said rotary members to produce reciprocating relative rotary motion between them, the direction of rotation of said first rotary member being simultaneously and relatively opposite to that of said second rotary member, said film having one end adapted to be secured to said second rotary member and an opposite end adapted to be secured to said first rotary member so that when relative rotary motion is produced between said rotary members in one direction of reciprocation one surface of said film moves into contact with said image-bearing surface, first source of charge migration means disposed adjacent to said first rotary member to induce an electrostatic charge pattern on the opposite surface of said film when said one surface of said film moves into contact with said image-bearing surface, and second source of charge migration means disposed adjacent to said second rotary member to induce an electrostatic charge pattern on said one surface of said film when said rotary members are rotated in an opposite direction of reciprocation and said film is separated from said image-bearing surface. 2. Apparatus as described in claim 1, wherein: said image-bearing surface is the surface of a recording element, and said recording element is secured to said first rotary member. 3. Apparatus as described in claim 1, wherein: said rotary members comprise elongated cylinders having electrically insulating surfaces, each of said cylinders is disposed on a separate shaft for rotation thereabout, said shafts are parallel to each other, and said means to produce reciprocating relative rotary motion between said rotary members are coupled to said rotary members through said shafts. 4. Apparatus as described in claim 1, wherein: said ends of said film are secured to said rotary members so that said film is unwound from said second rotary member and wound around said first rotary member, over said image-bearing surface, during one direction of reciprocation, and said film is unwound from said first rotary member, separating said film from said image-bearing surface, and

means to ground said wetted sponges,

means to urge said grounded wetted sponge in said first means against said opposite surface of said film. whereby to induce a charge pattern thereon, of opposite polarity to said original charge pattern, when said original charge pattern is on said imagehearing surface. and

means to urge said grounded wetted sponge in said second means against said one surface of said film, whereby to induce a charge pattern thereon of the same polarity as that of said original charge pattern. 

1. Apparatus for reproducing, on an electrically insulating film, an electrostatic charge pattern in an intensified form conforming substantially in configuration to an original electrostatic charge pattern on an electrically insulating imagebearing surface, said apparatus comprising: first and second rotary members having axes disposed substantially parallel to each other, means to dispose said image-bearing surface on at least a portion of said first rotary member, means coupled to said rotary members to produce reciprOcating relative rotary motion between them, the direction of rotation of said first rotary member being simultaneously and relatively opposite to that of said second rotary member, said film having one end adapted to be secured to said second rotary member and an opposite end adapted to be secured to said first rotary member so that when relative rotary motion is produced between said rotary members in one direction of reciprocation one surface of said film moves into contact with said image-bearing surface, first source of charge migration means disposed adjacent to said first rotary member to induce an electrostatic charge pattern on the opposite surface of said film when said one surface of said film moves into contact with said image-bearing surface, and second source of charge migration means disposed adjacent to said second rotary member to induce an electrostatic charge pattern on said one surface of said film when said rotary members are rotated in an opposite direction of reciprocation and said film is separated from said image-bearing surface.
 2. Apparatus as described in claim 1, wherein: said image-bearing surface is the surface of a recording element, and said recording element is secured to said first rotary member.
 3. Apparatus as described in claim 1, wherein: said rotary members comprise elongated cylinders having electrically insulating surfaces, each of said cylinders is disposed on a separate shaft for rotation thereabout, said shafts are parallel to each other, and said means to produce reciprocating relative rotary motion between said rotary members are coupled to said rotary members through said shafts.
 4. Apparatus as described in claim 1, wherein: said ends of said film are secured to said rotary members so that said film is unwound from said second rotary member and wound around said first rotary member, over said image-bearing surface, during one direction of reciprocation, and said film is unwound from said first rotary member, separating said film from said image-bearing surface, and wound around said second rotary member during an opposite direction of reciprocation.
 5. Apparatus as described in claim 1, wherein: said film comprises a sheet of plastic material, a plurality of holes are formed along opposite edges of said sheet, and said rotary members are formed with a plurality of sprockets to engage said holes in said film during the reciprocation of said rotary members.
 6. Apparatus as described in claim 1, wherein: each of said first and said second source of charge migration means comprises a receptacle having a wetted sponge therein, means to ground said wetted sponges, means to urge said grounded wetted sponge in said first means against said opposite surface of said film, whereby to induce a charge pattern thereon, of opposite polarity to said original charge pattern, when said original charge pattern is on said image-bearing surface, and means to urge said grounded wetted sponge in said second means against said one surface of said film, whereby to induce a charge pattern thereon of the same polarity as that of said original charge pattern. 